Ultra-high brightness LED flashlight

1. Circuit Principle and Characteristics

The principle circuit diagram of the ultra-high brightness LED flashlight is shown in the attached figure. In the figure, VT, R and T form a high-frequency pulse oscillator, which inverts the 1.5V DC power supply into a high-frequency pulse AC. After being stepped up by the pulse transformer T, it is rectified and filtered by VD and C to become a higher DC voltage to light up the LED. In fact, this DC converter is a self-excited oscillation flyback DC converter. The working principle is as follows:

After the power is turned on, the power supply provides base current to VT through L1b and R, VT starts to conduct, the collector current Ic increases, and VT gradually saturates and conducts. At this time, L2 induces a voltage, but the voltage polarity is negative at the top and positive at the bottom, VD cannot conduct, and the power supply energy is converted into electromagnetic energy and stored in the pulse transformer T: After VT is saturated, since the current in the inductor cannot change suddenly, Ic drops, and a higher voltage with positive at the top and negative at the bottom is induced on L2. At this time, VD conducts and charges C, and then lights up the LED, and the inductor magnetic energy is converted into electrical energy to supply the load (LED). VT is equivalent to a switch, T is an energy storage element, VT is alternately turned on and off, and the low-voltage DC power supply is boosted to high-voltage DC. This is the working principle of the DC converter.

2. Selection and debugging of components

In the circuit, the pulse transformer T is the key component, and it should be wound with a high-permeability magnetic ring. This is a power ferrite that has the characteristics of adapting to high frequency and high power. The magnetic ring can be removed from the old energy-saving lamp electronic ballast or the old computer motherboard. Generally, it has high permeability and can meet the requirements. It is advisable to use a larger magnetic ring. It is not easy to wind a magnetic ring that is too small. L1 is wound with 10 turns of ordinary single-strand insulated wire, and tapped at 6 turns to divide L1 into two sections, L1a (6 turns) and L1b (4 turns). L2 is wound with the same wire for 10 to 12 turns. If the single-strand insulated wire is difficult to wind, it can also be wound with high-strength enameled wire.

VT uses 3DD13003 or MJE13003 commonly used in electronic ballasts, with HFE≥20, and R uses 100Ω ordinary gold film resistor. VD uses IN4148 switch tube, and it would be better if high-frequency rectifier tube FR107 is used. LED uses LED with a diameter of 8mm to 10mm. If ordinary 5mm LED is used, 2 to 3 can be used in parallel. LED tubes with good performance parameter consistency should be selected to prevent uneven brightness.

Since the circuit is simple and uses few components, there is no need to use a printed circuit board. You can directly connect the components. You can also use a knife to carve out a small piece of printed circuit board and install it in the flashlight.

The same-named ends of the T windings cannot be connected incorrectly. The same-named ends have been marked with black dots in the circuit. The same-named ends of L1 and L2 are the starting ends when L1 and L2 are wound. After the circuit is welded, it must be carefully checked to confirm that the circuit is correct before the power supply can be turned on for debugging. Debugging is very simple. Connect the current range of the multimeter in series to the power supply and adjust the total current to about 100mA. If the current is too large, it may be caused by the VT's amplification factor being too small or the T's magnetic ring being unqualified and needs to be replaced.

This circuit can also be used for teaching laser transmitters (electronic pointers) with 1.5v power supply and some small LED table lamps on the market. If a larger magnetic ring is used in this circuit, the number of turns of L1 and L2 is increased, the turn ratio of L2 to L1 is improved, VT is replaced with a larger power tube such as 3DD13005, VD and C are replaced with higher withstand voltage, and the power supply voltage is increased to 9v~12v, the improved circuit can be used as a simple DC high voltage generator.